The book, which will be published Tuesday, contends Sanders’ 2016 attacks “caused lasting damage, making it harder to unify progressives in the general election and paving the way for Trump’s ‘Crooked Hillary’ campaign.” Then Clinton adds archly, “I don’t know if that bothered Bernie or not.”

The crusty Vermont senator couldn’t resist answering in kind. In an appearance on CBS with Stephen Colbert, Sanders snipped, “Secretary Clinton ran against the most unpopular candidate in the history of this country, and she lost. And she’s upset about that. I understand that.”

> On another front in the never-ending Hillary-Bernie proxy war, the Democratic Party’s Unity Commission is currently exploring the role of caucuses and superdelegates during the 2020 campaign.

But, in a move that underscores the weakness of the national parties, the state of California is expected this week to move its primary from June to early March 2020. Not only would such a dramatic alteration in the political calendar give a massive edge to California candidates, it could also effectively disenfranchise most other states in choosing a nominee.

Security Shoulder Small Backpack Men's Fashion Chest Messenger Bag Trend A > There was a flurry of recent talk that Ohio Republican Gov. John Kasich and his Colorado Democratic counterpart John Hickenlooper were considering running for president and veep as independents in 2020.

Both governors, who are working together on health care reform, denied such bolt-their-party ambitions. But the rumors illustrated the continuing fascination with a plague-on-both-your-houses independent politics.

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Remember, all this has happened in the last two weeks.

A strong case can be made that both Republicans and Democrats stepped off the cliff in 2016 — and only now are we grappling with the full implications of their plunge.

As much as ill-fated former Republican National Committee Chairman Reince Priebus tried to mask it, Trump’s nomination was nothing short of a hostile takeover of the GOP. Of course, Sanders battled Clinton all through the primaries without ever deigning to join the Democratic Party.

The July 2016 publication by WikiLeaks of hacked emails from the Democratic National Committee helped convince Sanders’ supporters that the fix had been in at the DNC.

But what few news stories at the time conveyed was how feeble the DNC had become with Debbie Wasserman Schultz as party chairwoman.

In a sense, the rise of super PACs turned both national party committees into afterthoughts.

With independent funders like Mercer and the Koch brothers on the Republican side and free-spenders like Tom Steyer for the Democrats, congressional candidates no longer look to the DNC and RNC for a major infusion of funds. What party funds exist mostly flow through the House and Senate campaign committees on both sides.

Small Bag Men's Backpack A Chest Shoulder Trend Messenger Security Fashion But it would be a mistake to underestimate the resilience of the two-party system.

If Trump truly had cut his ties with the GOP leadership on Capitol Hill, then congressional Republicans would be taking bold steps at this moment to aggressively investigate the president’s alleged ties to Russia. At minimum, there would be a serious look at whether the Trump family (including son-in-law Jared Kushner) was personally profiting from government service.

All glib talk about independent races for the White House ignore the obstacle that prevented Mike Bloomberg from running in 2016 — the Constitution. As long as a deadlocked presidential race is settled in the House, it is hard for an independent candidate to map a route to victory.

Political parties have endured vicious infighting before. The rise of Barry Goldwater ripped the Republicans apart in 1964 — and the Democrats soon bitterly split over Vietnam.

But the Electoral College and the lack of proportional representation in congressional elections means it will take more than Donald Trump and a few bad years to destroy the two-party system.

Roll Call columnist Walter Shapiro is a veteran of Politics Daily, USA Today, Time, Newsweek and The Washington Post. Follow him on Twitter @MrWalterShapiro.